No Return Data Checks on Chainlink's latestRoundData() Might Return Stale Prices

[code423n4]

Lines of code

https://github.com/code-423n4/2022-08-frax/blob/c4189a3a98b38c8c962c5ea72f1a322fbc2ae45f/src/contracts/FraxlendPairCore.sol#L524
https://github.com/code-423n4/2022-08-frax/blob/c4189a3a98b38c8c962c5ea72f1a322fbc2ae45f/src/contracts/FraxlendPairCore.sol#L532

Vulnerability details

Impact

The _updateExchangeRate function of FraxlendPairCore contract gets price using
chainlink latestRoundData function. However it lacks the check on the return data and
this might lead to stale prices.

Proof of Concept

./FraxlendPairCore.sol:524:            (, int256 _answer, , , ) = AggregatorV3Interface(oracleMultiply).latestRoundData();
./FraxlendPairCore.sol:532:            (, int256 _answer, , , ) = AggregatorV3Interface(oracleDivide).latestRoundData();

Tools Used

Manual Analysis

Recommended Mitigation Steps

I recommend adding checks on the return data as following.

(uint80 roundId, int256 _answer, , uint256 updatedAt, uint80 answeredInRound) = AggregatorV3Interface(oracleMultiply).latestRoundData();
require(answeredInRound >= roundId, "Stale Price");
require(updatedAt != 0, "Round Not Complete");

[0xA5DF]

Out of scope, same as #361

[amirnader-ghazvini]

Duplicate of #179